I've had both and carried both for EDC. Don't have either one of them anymore, but here are my thoughts on them. Both knives were tough and durable enough to do anything I would ask of a folder. That includes going from house and garden chores to working in a warehouse cutting strapping material and some cardboard to dayhikes and camping.
For me, and YMMV as always, the Rift was more comfortable to carry and use because of the rounded scales and lighter weight. The AXIS lock on the Rift worked flawlessly, as all of my AXIS locks have. The Rift was probably the sharpest BM I've gotten new except my Ritter Grips, and it got sharper when introduced to my Sharpmaker and strop. I enjoyed carrying and holding the Rift more than the 350. The Rift came new with a centered blade and no h/v BP. The rest of the F&F was excellent as well.
The 350 I had was a KW exclusive S30V satin finish. I noticed right away that it was heavier than I usually carry and the flat sided scales made it one of the less comfortable knives that I've carried and used. That is a personal preference, however, and that was my only objection to the 350. I don't normally like recurves but I didn't really notice it on the 350, sort of like the gentle recurve on the old 14210's. My 350 came centered, the blade fired fast & hard, the lockup was just the way I like liner locks; all of the liner was engaged on the blade tang, and the edge was as sharp O-O-B as the Rift was. No F&F issues at all with the 350.
The 350 felt a little more solid to me, but that's probably just based on visual perception and the heavy, blocky feel when holding it. AXIS lock vs. liner lock? For a knife like this with heavy or outdoor use, I'd prefer a dependable and well-made liner lock. I just don't trust spring-activated locks when simpler systems are available and are just as dependable. I've never had an issue with either type of lock, so I'll most often go for the simplest solutuion in a situation like that.
Both knives responded well to my Sharpmaker and strop block and neither blade suffered any damage from my use, so I have no preference there. In the end, it may come down to the dart board for you to pick the one you want. I believe the Rift is disco'd, so if being able to replace a lost or damaged knife with the same thing is important to you, you may want to stick to the 350.
Good luck.